The invention relates to a wheel for vehicles, in particular motor vehicles, having an arrangement including screws or nuts having the purpose of fastening a wheel disc made of fiber composite material to a vehicle hub.
A wheel for motor vehicles has, according to the prior art, a wheel disk made of metal, in particular steel or aluminum, which is embodied as a pressed or cast part. The wheel also includes an arrangement for fastening the wheel disk to the vehicle axle, wherein this arrangement is generally composed of screws which engage in corresponding threaded holes on the vehicle axle. However, it is also known to arrange stay bolts on the vehicle axle and to fasten the wheel disk by way of nuts. Four or five screws or nuts which are distributed over the circumference are customary. Such wheels can have, in addition to the wheel disk and the arrangement for fastening it, also further elements, for example wheel caps, cover plates or the like. The wheel disk which is composed of metal has sufficient strength and stability. The wheel brake is usually provided adjacent to the wheel disk and can be embodied as a disk brake or drum brake and is fastened to the axle housing of the vehicle axle or to a part of the axle suspension.
It is known that when the brake is activated frictional heat is generated which heats not only the elements of the wheel brake but is also transmitted to other adjacent parts. The heat which is output to the wheel disk does not adversely affect the strength and stability of the wheel disk, especially since a certain degree of cooling of the elements of the wheel brake and of the wheel disk also takes place during driving. This cooling can be made more difficult if the wheel disk is subjected to the effects of dynamic wind only to a certain extent since a wheel cap made of plastic or the like is used. Also, owing to the cramped installation conditions in the field of modern motor vehicles, the cooling of elements of the wheel brake is comparatively poor. Since the wheels are some of the unsprung masses of a motor vehicle, efforts are made to reduce these masses by using specifically lightweight metals, in particular aluminum.
DE 30 47 837 A1 describes a vehicle wheel having a wheel disk made of synthetic plastic, in particular made of plastic which is reinforced with glass fibers. In this context, the wheel disk is assigned a washer made of steel which has projections or radial webs on its side facing the vehicle hub. The fastening device is composed of screws which both penetrate the wheel disk and the washer and engage in the vehicle hub. The wheel disk which is composed of plastic has a central opening, through which cooling air from the exterior of the wheel can be sucked in. The driving of the cooling air is carried out through radial webs in conjunction with the rotating wheel. The washer made of steel covers only part of the wheel disk which is composed of plastic.
The invention is based on the concept of using a wheel disk made of plastic. It is possible to use, in particular, a fiber-reinforced plastic. A material is then used whose specific weight differs considerably from that of metals. However, such a plastic has the disadvantage that it is a poor conductor of heat, that is to say, as it were, it constitutes an insulating body. Given a considerable input of heat, this adversely affects the strength of the wheel disk. The different thermal expansion of plastics, in particular of carbon-fiber-reinforced polymers and metallic substances in the wheel screwing arrangement, gives rise to intrinsic thermal stresses when heating occurs, for example as a result of the brake. The bearing face between the wheel base body and the friction cap/wheel driver is thus highly thermally stressed. The poor conduction of heat of many plastics can then result in accumulation of heat, which can have a negative effect on the material plastic. Furthermore, customary metallic inserts in the region of the screwing arrangement must be electrically isolated from a carbon-fiber-reinforced plastic in order to avoid contact corrosion.
The object of the invention is to remedy these disadvantages by providing a particular device for fastening a wheel disk made of plastic.
This and other objects are achieved according to the invention by a wheel for a vehicle, having a rim which is intended to receive a tire, and a wheel disk which is connected thereto and is made of fiber composite material. An arrangement, which has screws or nuts and has the purpose of fastening the wheel disk to a wheel hub is provided, for which purpose the wheel disk has axially directed openings for the passage of the screws or threaded bolts for screwing onto the nuts. The arrangement includes, for each opening of the wheel disk, an insulating body, a bushing and a washer, each with a central opening which surround the breakthrough in the wheel disk in a U shape. The bushing bears, as a frame, against the inner circumference of the opening, and the insulating body and the washer at least partially cover the wheel disk in the radial direction while bearing against the frame and against the wheel disk, in each case on one side of the wheel, with the insulating body directed toward the inside of the wheel, and the washer directed toward the outside of the wheel. In this context, the insulating body can be composed at least partially of ceramic material.
If positively locking, frictionally locking or materially joined insulating bodies or ceramic inserts are introduced in the region of a wheel screwing arrangement in this way, this has the advantage that the ceramic material thermally insulates and, as a result, protects the plastic of the wheel disk against damage by high temperatures. Ceramic is also non-critical with respect to settling and creepage, even under temperature effects. As electrical insulators, ceramic inserts additionally avoid galvanic corrosion. For example ZiO2 is appropriate as a ceramic material. The ceramic material is then selected such that it is a thermal and galvanic insulator.
Preferred embodiments of the invention provide that the bushing and the washer are composed of ceramic material or of metal. In this case, the bushing and washer can advantageously also be embodied in one piece. Alternatively, the bushing and the insulating body can be embodied in one piece. If the wheel disk and the bushing then form a conical seat with one another, and the insulating body and the bushing possibly also form a conical seat with one another, such a conical attachment face has the advantage that a centering effect for the wheel disk is provided by the fastening device. Conical centering and support faces also contribute to enlarging the contact faces. Direct contact between the screws or nuts of the screw fastening and the wheel disk made of plastic is also avoided by the fastening device.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.